Logging Handlers Empty - Why Logging TimeRoatingFileHandler doesn't work

问题

So I do logging.config.fileConfig to setup my logging from a file config that has console and file handler. Then I do logging.getLogger(name) to get my logger and log. At certain times I want the filehandler's filename to change i.e. log rotate (I can't use time rotator because of some issues with Windows platform) so to do that I call logger.handlers - it shows an empty list, so I cant close them!! However when I step through the debugger, its clearly not empty (well of course without it I wouldn't be able to log right)

Not sure whats going on here, any gotchas that I'm missing?

Appreciate any help. Thanks.

回答1:

It seems you need to correctly get the root logger:

logger = logging.getLogger(__name__)
handlers = logger.handlers[:]
print('module {}'.format(handlers))
print('module {}'.format(logger.hasHandlers()))

logger = logging.getLogger('root')
handlers = logger.handlers[:]
print('root {}'.format(handlers))
print('root {}'.format(logger.hasHandlers()))

logger = logging.getLogger()
handlers = logger.handlers[:]
print('blank {}'.format(handlers))
print('blank {}'.format(logger.hasHandlers()))

output:

module []

module True

root []

root True

blank [<logging.handlers.RotatingFileHandler object at 0x108d82898>, <logging.StreamHandler object at 0x108d826d8>]

blank True

回答2:

Firstly the issue is that, if you use a config file to initialise logging with file and console handlers, then it does not populate logging.handlers list, so you can not iterate over it and close+flush the streams prior to opening new one with a new logging file name.

If you want to use TimeRotatingFileHandler or RotatingFileHandler, it sits under logging/handler.py and when it tries to do a roll over, it only closes its own stream, as it has no idea what streams the parent logging (mostly singleton) class may have open. And so when you do a roll over, there is a file lock (file filehandler) and boom it all fails.

So the solution (for me) is to initialise logging programatically and use addHandlers on logging, which also populates logging.handlers [], which I then use to iterate over my console/file handler and close them prior to manually rotating the file.

It to me looks like an obvious bug with the logging class, and if its working on unix - it really shouldn't.

Thanks everyone, especially @falsetru for your help.